PROJECT SUMMARY/ABSTRACT Liver cancer is one of the most common and lethal cancers; hundreds of thousands of new cases occur yearly with only a 20% chance of survival one year past diagnosis. Furthermore, the mortality rate of liver cancer is increasing beyond most other cancers. Hepatocellular carcinoma (HCC) makes up to 70-85% of all cases of liver cancer, and currently only the multi-targeted kinase inhibitor Sorafenib is approved as therapy outside of surgery and radiation. Sorafenib was first approved in 2007, and since this time all subsequent approaches have thus far failed to improve upon an average 2.8 month extension in overall survival for liver cancer patients. A significant challenge in improving upon Sorafenib is that the mechanism of this drug, in particular the functional basis for efficacy and toxicity, remains poorly understood in HCC. Although originally developed as a RAF-kinase inhibitor, it is unlikely that RAF inhibitory activity is responsible for patient responses to Sorafenib. VEGFR has been suggested as an important target, yet other more potent VEGFR inhibitors have failed to extend life in comparison with Sorafenib. Due to the multi-kinase activity of Sorafenib, I hypothesize Sorafenib is modulating both undesirable anti-targets as well as desirable targets. I furthermore posit that it is the balance between the targets and anti-target activities of Sorafenib that largely determines the therapeutic index of this drug. Here, I propose to evaluate a focused library of Sorafenib analogs (Sorafelogs) to uncover structure-activity relationships (SAR) that will be used to identify functional targets and anti-targets of Sorafenib. We have already identified striking SAR with preliminary compounds in the context of HCC cell line models, and are using cross-comparison of these structurally related compounds to uncover the mechanistic basis for growth inhibition and the induction of apoptosis by Sorafenib. Putative physical targets will be validated using biochemical and genetic approaches. Furthermore, we have identified a Sorafelog, which we term AD80, which is 10 to 100-fold more cytotoxic on HCC cell lines than Sorafenib. However, in whole animals, this compound is well-tolerated suggesting limited side-effects. We will explore both Sorafenib and AD80?s targets and anti-targets using pathway analysis on cell line models, and a whole-body fly genetic model of HCC. These findings should lead to an optimized version of Sorafenib that would inhibit drivers (ie. targets), but avoid suppressors (anti-targets). These studies will provide a greater mechanistic understanding of viable therapeutic options for this heterogeneous disease, and furthermore will provide compounds that ideally reduce toxicity and increase efficacy in HCC. This will also help to better select patients with the highest probability of responding to Sorafelogs, and decrease the costs impaired by liver cancer.